In the prior art there are known various methods for improving the anti-flame properties of thermoplastic polymers. One of the most recent of such methods consists in admixing with the polymer a combination of an ammonium phosphate or other organic phosphorus containing compound and of one or more organic substances capable of yielding, by thermal decomposition, uninflammable gaseous products (water, carbon dioxide, ammonia, nitrogen) and carbonaceous residues. The aforementioned organic substances consist of nitrogen containing compounds (e.g. melamine, cyanuric acid, dicyandiammide, urea, ethylenurea and others) or of mixtures of a nitrogen containing compound and a polyalcohol.
In Italian patent application No. 27.520 A/77 there have been described and claimed polymeric self-extinguishing compositions consisting of a thermoplastic polymer and an anti-flame additive consisting of:
(A) an ammonium or amine phosphate; PA1 (B) one or more organic compounds capable of yielding, by thermal decomposition, uninflammable gaseous products and carbonaceous residues; and PA1 (C) an ester of isocyanuric acid of general formula: ##STR2## wherein R.sub.1, R.sub.2, R.sub.3 either like or different from each other, are linear or branched alkylene groups having from 1 to 6 enchained carbon atoms, while Z.sub.1, Z.sub.2, Z.sub.3 are --OH groups or ##STR3## the ratio by weight (B)/(C) ranging from 10:1 to 1:10, and components (A) and (B)+(C) each being used in a quantity of 5%-30% by weight on the total of the composition. PA1 (a) at least one organic compound selected from the group consisting of PA1 (b) an epoxyalkylester of isocyanuric acid of the formula: ##STR4## wherein n is an integer from 1 to 3; the reaction being effected according to a molar ratio (a):(b) comprised between 3:1 and 0.1:1.
In such compositions the substitution of a part of the second additive with the isocyanuric ester has the effect of boosting the anti-flame effectiveness of the (A)+(B) combinations.
In the above cited patent application it was specified that components (B) and/or (C) are used preferably in a form insoluble in water, that is, in the cross-linked state, the cross-linking being carried out according to known techniques. For example, when component (B) is a nitrogen containing compound, such as melamine, urea or dicyandiamide, it can be used in the form of a condensation product with formaldehyde; when component (C) is a hydroxyalkylisocyanurate, it can be made to react with an organic polyisocyanate or with formaldehyde, and when it is an epoxyalkylisocyanurate, one can revert to a cross-linking with one of the known curing agents for epoxy resins, such as a polyamine.
In the above-cited patent application it was, moreover, asserted that according to an even more preferred form of embodiment components (B) and (C) are cross-linked together under formation of a single macromolecular structure: thus for instance, instead of using a combination of a reaction product tris(2-hydroxyethyl)isocyanurate/formaldehyde and of a reaction product melamine/formaldehyde, there may be used a single resin tris(2-hydroxyethyl)isocyanurate/melamine/formaldehyde resin which is prepared by reacting under heat an aqueous solution of formaldehyde, acidified with sulphuric acid, first wtih tris (2-hydroxyethyl) isocyanurate and subsequently with melamine, said reaction being carried out at two distinct temperatures, for a total time of about 7 hours.